Heat energized vapor adsorbent pump

ABSTRACT

A solid matrix of microporous adsorbent is utilized to provide a barrier between two bodies of a gaseous mixture of which at least one constituent is a sorbable vapor. Appropriate application of heat at the opposing interfaces of the adsorbent barrier produces a partial pressure differential across the barrier. The adsorbent material is energized from a convenient heat source; for example, solar energy. The vapor pump of the invention may be used for environmental refrigeration and may be of the open or closed type. Other uses for the vapor pump are for producing a supply of pure water from low vapor content air or for drying air by removing the vapor content.

This is a division of application Ser. No. 789,482, filed on Apr. 21,1977.

FIELD OF THE INVENTION

The invention relates to a heat energy operated vapor pump and its usein cooling systems of open or closed loop types and in water reclamationsystems. The pump is especially adaptable for utilizing the heat energyfrom a solar source for its operating energy source.

BACKGROUND OF THE INVENTION

There has long been a need for control of the living environment interms of temperature and humidity. The need extends to requirements forcontrol of the environments in which man lives and works (his shelter),and to sub-environments which house and preserve perishables. Somecommercial applications of such systems include the manufacture of ice,environmental control of public and office buildings, hotels, stores andfactories.

Two basic types of refrigeration systems exist in the prior art;intermittant and continuously operating systems. The continuouslyoperating system is prevalent in modern use. Within the constraint ofcontinuously operating refrigeration systems, there are two majorsub-types. Absorbent systems (see FIG. 3) such as the Platers-Munterstype (marketed by Servel, Inc.) and vapor compression systems (seeFIG. 1) which widely prevail in the United States. These two sub-typesshare some common features. Each is provided with condenser heatexchanger 10 for converting relatively high temperature, high pressuregas to a warm liquid state, each utilizes expansion valve 14 forcontrolled expansion of the warm liquid to a cooler gas state and eachprovides evaporator heat exchanger 2 for extracting heat from a volumewhich is to be environmentally controlled. Heat pump versions of atleast the compressor type systems are supplied with reverse cyclecapability for heating the volume to be environmental controlled. Bothsystems depend upon the relatively high efficiencies available whenrefrigerant is converted from a gas to a liquid state and from a liquidto a gas state based on the "leverage" provided by high latent heats ofvaporization and condensation.

The major features of the two systems may be distinguished by inspectionof FIGS. 1 and 3. Either system requires an energy input; compressor 6requiring rotary motion, generally suppled by electric motor 5, and theabsorbtion system requiring relatively high temperature source of heat30 for desorption (FIG. 3).

The absorption system as commercialized by Servel, Inc. (FIG. 4)utilizes an absorbent, which may be water, a refrigerant, which may beammonia, and a pressure equalizing gas, which may be hydrogen. While thepartial pressure of the refrigerant varies from the high pressure sideof the system to the low pressure side of the system, the introductionof hydrogen gas provides compensation providing for equalization of thetotal pressures on each side of the system thereby eliminating the needfor a fluid pump and for a second throttling valve. The Servel, Inc.,version of the absorption refrigeration system thereby avoids the use ofany mechanical moving parts at all and allows for gravity and convectionflow of the various liquids and vapors in the closed system.

Referring to FIG. 4, generator 200 contains a saturated solution ofammonia absorbed in water. Heat source 202 supplies the energy requiredto drive ammonia gas (represented by small circles) out of theammonia/water mixture 204. Ammonia gas is released and rises in conduit206 to separator 208. Water is carried along by a percolation processand the mixture is separated in separator 208. The relativelyammonia-free water leaves separator 208 in conduit 210 while theliberated hot ammonia gas rises in conduit 212 to condenser 10. The gasis reduced in temperature by condenser 10 and is converted to a warmliquid at liquid trap 214. When the warm ammonia liquid passes throughliquid trap 214, it sees a reduced partial ammonia vapor pressure inconduit 216 and evaporator 2. It is then able to expand at the lowerpressure, becoming a relatively cold gas in evaporator 2. Heat fromvolume 18 is absorbed by the cold gas in evaporator 2, thereby coolingvolume 18. Conduit 218 carries the warmed ammonia gas to absorbers 220and 222.

The low ammonia content water from separator 208 is cooled in absorbers222 and readily absorbs the warm ammonia gas from conduit 218. Theammonia-bearing water flows by gravity feed to absorber 220 and thenthrough conduit 224 back to generator 200, there to begin the cycle overagain.

Conduit 226 is filled with an inert or neutral gas such as hydrogen. Thehydrogen also infiltrates the low pressure side of the system; that is,conduits 216, 218, and 222, upper portion of absorber 220 and absorbers222. The partial pressure of hydrogen plus the partial gas pressures areadditive to the total system pressure so that the total system pressureis equal in all portions of the system.

Systems utilizing dessicant beds have been described in the prior art.Some are of the type which require physical transportation of the bed,such as that described in "Solar Energy Thermal Processes", John Wileyand Sons, Duffie and Beckman, pages 341-3, and others attainintermittant operation only. Faraday demonstrated an intermittantabsorber-vaporizer utilizing silver chloride and ammonia in 1824. SeeFIG. 2. Absorber 33 (silver chloride), which had been exposed to dryammonia gas in one end 34 of inverted "V" test tube 36, was heated. Whenopposite end 38 of "V" shaped test tube 34 was cooled by insertion inwater 40, liquid ammonia 42 was condensed at the cooled end. When theheat was removed from the absorber end of the test tube, Faraday noticedthat the liquid ammonia in the other end boiled violently, changing backto a vapor which was reabsorbed by the silver chloride absorber. Thelatent heat of vaporization caused the liquid ammonia end of the testtube to be very cold.

Intermittant absorbtion systems were popular in the 1930's. The Trukholdrefrigerator distributed by Montgomery Ward and the Icy Ball systemmanufactured by the Crosley Corporation were examples of this type.("Modern Refrigeration and Air Conditioning", Althouse and Turnquist,The Goodheart-Willcox Co., Inc., 1960.)

The ammonia/water/hydrogen combination employed in the Servel system istypical of absorption systems (as contrasted to adsorption systems).There, water is used as an absorbent and absorption is of a chemicalnature. In contrast, other systems utilize physical adsorbents, one ofthe most common being silica gel. Silica gel is a microporous inertmaterial. It is characteristic of the material that each granual isliterally full of interconnected molecular sized holes which provide anenormous amount of internal surface area. It is also characteristic ofsilica gel that transient adsorption rates are very rapid and the highrates of diffusive flow are attributed to strong surface diffusionphenomena. When sorbable vapors are adsorbed into high internal surfacearea microporous media, the diffusive flux is greatly increased bysurface diffusion of mobile adsorbed films in a concentration gradient.

Another material which exhibits similar characteristics is Vycor porousglass as manufactured by the Corning Glass Works, Corning, N.Y.

E. R. Gilliland, R. F. Baddaur and H. H. Engel reported the results ofan investigation of gas flow by adsorption in "Flow of Gases ThroughPorous Solids Under the Influence of Temperature Gradients", AmericanInstitute of Chemical Engineers Journal, 8 A.I.Ch.E.J. 530, September,1962. Results recorded there indicate a diffusion gas flow from a coldto a hot surface through a porous solid such as Vycor. K. G. Denbigh andG. Rauman have suggested that such a flow through a thin rubber membranemay occur in the face of adverse pressure differentials, although, aswell known in the art, the diffusion rate is as much as 1,000 timesslower than the diffusion through Vycor porous glass. 210A Proceedingsof the Royal Society (London) 518 (1951). Gilliland et al, supra, at530, stated, "both the gas phase and surface flows are from the cold endto the hot end of the porous solid." They suggested, in conclusion,supra, at page 535, "Isobaric permeabilities of the pure adsorbed gasesinvestigated are considerably higher than the values predicted fromcorrelation based on free-molecular flow data. The higher rates of floware attributed to a net migration of adsorbed gas along the surface ofthe pores." This high flow rate migration phenomona is not noticable innon-hygroscopic materials.

The phenomona reported by Gilliland et al, supra, may be betterunderstood by means of the following: Since the adsorption process isexothermic upon occurance, the application of heat at one adsorbentinterface provides the endothermic desorption of sorbate molecules andthe rejection of heat at the opposing interface provides the exothermicadsorption of the sorbate molecules. The addition of sorbate moleculesat the cold interface and the deletion of sorbate molecules at the hotinterface establishes a concentration gradient in the adsorbent thatdrives the diffusion of adsorbed vapors from cold to hot. Thisphenomenon is more generally described by the thermodynamics ofirreversible processes and is closely analogous to the thermoelectriceffect. In any overview, the predominate driving forces are provided forby the concentration gradients.

The conditions of the experiment described by Gilliland et al, supra,were such that the pressure was held constant and was far below thesaturation pressure of the vapors investigated.

Various means have been devised to provide heating or cooling from thesolar energy source. One of the major problems which limits commercialfeasibility of these systems is a very high initial cost as the resultof schemes used to raise the effective temperature of the energy sourceby some sort of heat concentration means. The temperature increase hasbeen found to be desirable and necessary in prior art systems in orderto provide more efficient heat transfer characteristics in theheating/cooling systems.

Prior art cooling systems may be classified as evaporative orrefrigerant systems. The evaporative systems are very ineffective unlessoperated in dry climates. Mohr's U.S. Pat. No. 2,202,019 is an exampleof such a system. Altenkirch's U.S. Pat. No. 2,138,691 teaches the useof silica gel and/or wood shavings as adsorbents used for the removal ofmoisture from air.

In solar engergized systems, some means must be supplied to provide asource of heat energy at those times when solar energy is unavailable oris in the short supply, i.e., at night or on overcast days. Lof's U.S.Pat. No. 2,680,565 teaches the use of a heat storage bed made of "aloose or spaced solid, such as sand, gravel or stacked brick, but whichmay be a fluid, such as tar, oil, water or the like." (U.S. Pat. No.2,680,565, Col. 6, lines 40-42.) The storage bed may be charged withheat energy at those times of relatively bright sunlight and may bedrawn upon as a source of heat energy when adaquate sunlight is notavailable.

Solar energy heating/cooling systems have been slow to receive publicacceptance because of their complexity and high initial cost and becauseof the general tendency for the systems to be bulky and inefficient.

SUMMARY OF THE INVENTION

These and other shortcomings of the prior art are overcome in accordancewith the present invention by utilizing the pumping capability of asolid adsorbent material exposed to a transverse temperature gradient inthe presence of a sorbate material due to "leverage" attained as aresult of sorbate diffusion. The vapor pumping action produced is usedto supply the vapor pressure differential which is accomplished by gascompression in a vapor compression refrigeration cycle. The efficiencyof the invention is effectively multiplied by the very high efficiencyof the diffusion through a solid adsorbent under the influence of atemperature gradient.

According to one aspect of the present invention a vapor pumping actionis produced by a solid adsorbent disposed between a low temperature-lowpressure refrigerant vapor and a higher temperature-higher pressurevapor of the same type.

According to another aspect of the invention, the diffusioncharacteristics of a solid adsorbent, positioned between a lowtemperature-low pressure sorbable vapor and a higher temperature-higherpressure vapor of the same type, acts to produce a pumping action fromthe low pressure-low temperature side to the higher temperature-higherpressure side. It will be clear to one skilled in the art that theadverse pressure is a partial vapor pressure.

According to still another aspect of the present invention, the pumpingaction of a solid absorbent, positioned in a refrigeration gasenvironment such that a combination pressure/temperature gradient existsbetween a cooled and a heated side, acts to provide the necessary vaporpressure differential which is accomplished by gas compression in arefrigeration system of the vapor compression type.

According to yet another aspect of the present invention, a solidadsorbent is used to pump water vapor against a vaporpressure/temperature differential.

According to an additional aspect of the present invention, a solidadsorbent is used in an open or closed refrigeration system to pumprefrigerant vapor from a cooler low vapor pressure side to a warmer highvapor pressure side.

According to another additional aspect of the present invention, a solidadsorbent is used to pump water vapor from a cooler low vapor pressureside to a warmer high vapor pressure side.

According to still another additional aspect of the present invention,solar heat energy is provided to warm a higher pressure side of a solidadsorbent to a higher temperature than a cooler lower pressure otherside to provide a temperature gradient for urging a diffusion pumpingaction of a vapor from the cooler lower pressure side to the warmerhigher pressure side.

According to yet another additional aspect of the invention, asupplementary neutral gas is utilized to equalize the total pressures onboth sides of a solid adsorbent being used to pump a vapor from a lowpartial pressure side to a high partial pressure side.

The foregoing and other aspects of the present invention will be morefully understood from inspection of the detailed description whichfollows and from the accompanying drawings in which:

FIG. 1 is a diagram of a prior art vapor compression cycle refrigerationsystem.

FIG. 2 is illustrative of the silver chloride-ammonia absorbentrefrigeration system experiments accomplished by Faraday in 1824.

FIG. 3 is a diagram of a prior art continuously operating absorptionrefrigeration system.

FIG. 4 is a simplified diagram of a prior art vapor absorbent cyclerefrigeration system as manufactured by Servel, Inc., incorporatinghydrogen gas as a pressure equalizing medium.

FIGS. 5 and 5a illustrate the vapor pump of the invention. FIG. 5b isillustrative of a series or cascade arrangement of two identical vaporpumps of the invention.

FIG. 6 is a diagram of the vapor pump of the invention in an idealizedembodiment of a closed cycle refrigeration system.

FIG. 7 is a diagrammatic illustration of a closed cycle refrigerationsystem using the pump of FIG. 5.

FIG. 8 is a diagram of the vapor pump of the invention in a typicalembodiment of an open cycle refrigeration system.

FIG. 9 is an illustration of the vapor pump of the invention whenutilized as a continuously operating dehumidifier for an enclosedvolume.

FIG. 10 is illustrative of a system for extracting pure water fromrelatively dry ambient air using the pump apparatus of FIG. 5.

FIG. 10a is a cross section of the apparatus of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

Referring first to FIG. 5, adsorbent layer 50 is held by support 52.Plenum 54 is formed between adsorbent 50 and heat exchanger 56. Heatexchanger 56 may be cooled by application of a water spray from sprayheads 57. Plenum 58 is formed between adsorbent 50 and heat absorber 60,on the opposite side. Heat absorber 60 is preferably covered bytransparent member 62 which may be made of glass. Support 64 serves tosupport heat absorber 60 and transparent surface 62 in a predeterminedrelationship with respect to adsorbent 50. Heat source Q₃, which may bethe sun, is arranged to radiate heat energy through transparent member62 into heat absorbent member 60. Heat absorber 60 may be surfaced onone side 68 with means for enhancing heat absorption qualities, such asblack paint or other highly absorbtive surface finish. The space betweenheat absorber 60 and transparent surface member 68 is preferably filledwith a low density gas or vacuum to inhibit loss of heat by convectionfrom heated absorber 60. Clearly, if a vacuum is used, the pressuredifferential across the glass will be significant and must be dealtwith. Of course, other means of reducing convective loss may also beused. Adsorbent 50 may be any of a number of different materials whichoperate as effective adsorbents. One such material which might be usedis silica gel. Some ceramic materials such as alumina or other metaloxides might be used and experiments indicate that Vycor porous glass asmanufactured by Corning Glass Works, Corning, N.Y., is a suitablematerial.

It will be understood that the surface areas of adsorber 50, heatexchanger 56, heat absorber 60 and transparent member 62 are set bydesign requirements of the particular application. Surface areas from afraction of a square inch to many thousands of square feet may berequired in different applications to provide the necessary diffusivemass flow required for the particular applications. The structuralrequirements of larger panels may be met by providing cellularstructural members or other structural systems for support of the large,flat surfaces. In the case of adsorber 50, if granular materials areutilized, they may be placed in the interstitial spaces of a cellularstructural member (not shown). The cellular member should preferably,have low heat conductance properties to prevent degeneration of thetemperature gradient across adsorber 50. It is also important that thethermal conductivity of adsorber 50 be relatively low for the samereason.

A description of the operation of the invention herebefore describedwill help the reader to understand the purpose of the various materials.Heat source Q₃ is used to warm surface 70 of adsorbent 50. This isaccomplished by means of radiant energy reaching heat absorber 60through transparent surface 62. The heat source may be any one of anumber of types and, of course, a number of other methods may be used toraise the temperature of surface 70 with respect to surface 72. Animportant heat source for this purpose is solar energy from the sun. Itis important to understand that surface 70 of adsorbent 50 is warmerthan surface 72. The positive temperature gradient across adsorbent 50is important to the operation of the invention. Surface 72 must becooler than surface 70 and, conversely, surface 70 must be warmer thansurface 72. Under these conditions a sorbate material, such as watervapor, may be introduced in plenum 54 in proximity to cooler surface 72of adsorbent 50. Materials such as silica gel are said to behygroscopic; that is, they have an affinity for water. They may alsohave an affinity for other vapors. The water vapor sorbate in an aircarrier is attracted to adsorbent 50. Adsorbent 50 is permeated with amyriad of micropores in the size range of from 10⁻⁶ to 10⁻⁷centimenters. There is a physical attraction between each of themicropores and the individual water vapor molecules in plenum 54. When amolecule of the water vapor comes in contact with one of the manyopenings in adsorbent 50 it is attracted therein. When a water vapormolecule is attracted into one of the micropores in adsorbent 50 it isphysically entrapped in the opening forming an adsorbed phase. Theresult in terms of heat energy is slightly greater than that which wouldoccur if an equivalent amount of water vapor were condensed to liquidform. When the adsorbed phase is formed, the heat of absorption isreleased. It is necessary to the operation of the invention that thisheat be dissipated in some manner. If it were not dissipated, surface 72of adsorbent 50 would warm up and the temperature gradient acrossadsorbent 50 would disappear. Therefore, heat exchanger 56 is used tocarry heat away from the sorbate carrier, typically air, in plenum 54.

FIG. 5a shows the cross section of the pump of FIG. 5 at reference line5a--5a. The air/vapor mixture in plenum 54 is channeled between baffles55 and baffles 55, in turn, provide structural support between adsorber50 and heat exchanger 56 and also provide for conductive heat flow fromadsorber 50 to heat exchanger 56. Baffles 55 are parallel to the mainflow of the air/vapor mixture in plenum 54, therefore contributing arelatively low impediment to the air/vapor flow. In some applications,it will not be necessary to enclose plenum 54 at the bottom side. (See,for example, FIG. 10.) Baffles 55 then may be utilized as fins for heattransfer to the ambient air.

In FIG. 5, the water vapor molecules in plenum 54 are represented assmall circles, while the air molecules are represented as arrows. Thearrows also indicate the preferred direction of flow of the watervapor/carrier mixture. It should be noticed that water vapor moleculesare being continually removed from the air carrier in plenum 54 becauseof their attraction to the adsorbent 50. The number of water vapormolecules shown at the upper end of plenum 54 is minimal.

So far the discussion has centered on the adsorbent characteristic ofmaterial such as silica gel. It will be well known to one skilled in theart that silica gel is a hygroscopic material that attracts water vaporout of air. It will be equally well understood that a given volume ofsilica gel has a limited capability for attracting water. Once thesilica gel volume is saturated with water it will no longer attract newwater vapor molecules. It is, therefore, a scheme of the invention todesorb water vapor molecules at opposite side 70 of adsorbent 50 therebyproviding additional capacity for adsorption of water vapor molecules atsurface 72 of adsorbent 50.

The desired additional capacity of adsorbent 50 to accept a continuousstream of water vapor molecules from plenum 54 is accomplished byremoving water vapor molecules from adsorbent 50 into plenum 58 on theopposite side of adsorbent 50. This is accomplished by warming surface70 of adsorbent 50 so that the liquid state water which has migratedthrough adsorbent 50 to surface 70 will be de-adsorbed in the form ofwater vapor molecules in plenum 58. It will be noted that at the lowerend of plenum 58 there is a dearth of water vapor molecules while at theupper end of plenum 58 the water vapor molecules are relatively moreplentiful. As in plenum 54, plenum 58 is represented as a conduit forboth air and water vapor. Again, as in plenum 54, the air is representedby arrows; the water vapor molecules are represented by small circles.Transparent member 62 and absorber 60 may extend beyond the lower end ofadsorber 50 so that the relatively dry air at the lower end of plenum 58is preheated before reaching surface 70 of adsorber 50. Liquid water inadsorbent 50 is constantly being de-adsorbed from surface 70 under theinfluence of the heat generated by heat absorber 60. There is a sensibleheat transfer from heat absorber 60 to adsorbent 50 surface 70. Theconversion of the water from the adsorbed state to the de-adsorbed vaporstate requires the heat of desorption, a concept which will be wellknown to one skilled in the art.

The invention as heretofore described may be thought of as a water vaporpump. However, the pumping action is not limited to the use of watervapor. Other materials which convert easily from gas to liquid state andvice versa might also be used. Typical of these are ammonia and Freon (atrademark of E. I. Dupont de Nemours & Company).

It will also be understood that materials other than silica gel andVycor porous glass may be serviceable as the microporous adsorbent. Forexample, oxides of aluminum and other metals may provide the necessaryhygroscopic and/or adsorbent characteristics.

Further, it will be understood that the usefulness of the pump of FIG.5, described herein, may be enhanced under some operating conditions bycascading the operations of a plurality of such pumps as shown in FIG.56. The mixture emitted from plenum 54 of pump 32 may be introduced intothe input end of plenums 54a and 58a of identical pump apparatus 32a.Since the partial vapor pressures would initially be equal in the twoplenums of second pump 32a, under the influence of a similar temperaturegradient, the second pump apparatus will proceed to cause still furtherbulk vapor flow from its cooler to its warmer side. The result is astill dryer mixture at the output of plenum 54a of second pump 32a. Thecascading technique may be carried on similarly to still more pumps in alike manner. Similarly, if the output of plenum 58 is introduced intothe inputs of plenums 54a and 58a of second identical pump 32a, a stillwetter mixture of air and water will be available at the output ofplenum 58a of second pump 32a.

The diffusion pumping action generated by the invention, as described,is capable of overcoming an adverse partial vapor pressure differentialbetween plenum 54 and plenum 58. Once this fact is accepted, it becomesclear that the invention may be used in a number of ways.

For example, referring to FIG. 10, the apparatus of the invention, withlittle modification, may be used to generate fresh water from lowhumidity air. Even in the very dry air conditions of the Southwesterndeserts of the United States, for example, where the ambient humidity isfrequently in the range of from five to ten percent, water vapor whichmay be contained in air 80 will be adsorbed into adsorbent 50. A verysmall air motion across surface 72 of adsorbent 50 is sufficient tosupply new, relatively moist air to replace the dry air which is createdwhen moisture vapor is adsorbed into adsorbent 50. Cooling fins 82, suchas shown in both FIG. 10 and FIG. 10a, may be utilized on the face ofadsorbent 50 to aid in rejection of the heat of adsorption from surface72. The heat of adsorption also causes air 80 to become less dense andrise along surface 72. This convective motion of the air in contact withsurface 72 assures a constantly refreshed quantity of moisture bearingair at surface 72. Of course, any movement of air 80 caused by naturalcauses, such as wind, will also enhance this effect. The heat ofadsorption is carried off, then, by both the motion of air 80 and, ifused, fins 82. This assures that surface 72 is adsorbent 50 stays closeto ambient temperature. The upper side of adsorbent 50 is heated, as hasbeen previously explained, by heat source Q₃ impinging on heat absorbingsurface 60 through transparent member 62, which may be glass.Utilization of careful design techniques, well known in the art, mayprovide a heat temperature gradient across adsorbent 50 in theneighborhood of 100° Fahrenheit since known flatplate collectortechniques may provide an operating temperature of about 200° Fahrenheitwhen the ambient is 100° Fahrenheit. This temperature gradient of 100°Fahrenheit is more than adequate to provide the pumping actionpreviously described. For example, if the device of FIG. 10 is operatedin an ambient temperature environment of 100° Fahrenheit, relativehumidity 10%, the partial vapor pressure at surface 72 will be equal toslightly less than 0.1 pounds per square inch. From a standardpsychrometric table it may be determined that in order for water tocondense out of air at a temperature of 100° Fahrenheit it is necessaryfor the partial vapor pressure to be 0.9492 pounds per square inch.Therefore, adsorbent 50 must have a partial vapor pressure gradient of0.8492 pounds per square inch between surface 72 and surface 70.Regardless of the total pressure in plenum 58 the partial pressure ofwater vapor in plenum 58 will cause water vapor to migrate to the top ofplenum 58 and thence down through condenser 74. Condenser 74 provides anambient temperature heat exchange to a sink of 100° Fahrenheit or areduction in the temperature of the vapor of nearly 100° Fahrenheitbelow the approximately 200° Fahrenheit temperature of the vapor at theinput to condensor 74. While the air/water vapor mixture in condenser 74is reduced to 100° Fahrenheit with a partial vapor pressure of 0.9492pounds per square inch, condensation occurs. Condensation forms water 78in container 76. It is useful to note that container 76 may be left openat the top. This means that if, for example, the device of FIG. 10 isdesired to be used for generating drinking water for farm or rangeanimals, the system becomes self-tending. Conduit 51 provides a returnpath to plenum 58 for facilitating free connective flow through plenum58. Barrier 79 prevents the air from condenser 74 from escaping to theoutside and assures that it is channeled back through conduit 51 toplenum 58.

Another significant use for the instant invention is suggested by a moreclassical use for hygroscopic materials such as silica gel. It is wellknown in the art to use silica gel or similar hygrocopic material toevacuate moisture from a closed volume. This has been done wherever adry environment is required, for example, for effective operation ofequipment such as sensitive electronic circuits. Generally, suchenclosures are sealed to help prevent migration of air and moisture fromthe environment into the enclosure. However, even the best sealingmethods are not one-hundred percent effective. Over a period of timesome moisture does migrate into the enclosure because the seal is notperfect. In order to minimize the effects of this problem, the prior artpractice has been to place a small amount of silica gel, a hygroscopicmaterial, into the enclosure at the time of sealing. Of course it isnecessary to purge the container of any moisture present at the time ofsealing in order for the procedure to be effective. The silica gel isplaced in the container in its dry state and serves only to capturewhatever water vapor enters the enclosure through the seal over thelifetime of the the seal. The problem presented by this system lies inthe fact that the silica gel has a limited capacity to adsorb moisture.Once this capacity is reached, the silica gel is no longer effective andthe vapor content within the enclosure begins to increase.

FIG. 9 is illustrative of the use of the invention to solve thisparticular problem. Enclosure 100 may be of the type generally used toprotect electronic equipment from an external environment. FIG. 9illustrates the insertion of hygroscopic window 102 in one surface ofenclosure 100. Window 102 may be of a material such as Vycor porousglass as manufactured by Corning Glass Works, Corning, N.Y. or any otherrigid hygroscopic material. Heat source 104 serves to heat the outersurface of window 102 to a higher temperature than the inner surface ofwindow 102 thereby setting up the requirements for vapor pumping from acooler inner surface to a warmer outer surface. Since window 102 isconstantly being regenerated by the desorption process at the outersurface, window 102 never becomes saturated with moisture vapor and forall practical purposes may be considered to have an infinite lifedependent only on the presence of heat source 104. In this manner, itbecomes possible to limit the buildup of moisture within enclosure 100for as long as is necessary.

It will be clear to one skilled in the art that by controlling thetemperature gradient across window 102, the moisure content in enclosure100 may be closely controlled in turn.

As has been previously described, FIG. 1 illustrates the well knownprior art vapor compression refrigeration system. Line 19 divides highpressure side, P_(H), of the system from low pressure side, P_(L), asshown. FIG. 3 illustrates a similar system wherein pump 6 and motor 5(FIG. 1) have been replaced by apparatus 28. Pump 22 of apparatus 28 isused solely for moving liquid from a low pressure to a high pressure. Asin FIG. 1, line 19 separates high pressure side, P_(H), from lowpressure side, P_(L), of the system. Pump 22 accomplishes no compressionof the vapor. As will be well known to one versed in the art, the systemof FIG. 3 is known as a vapor absorption system. For purposes ofillustration it may be considered that water and ammonia are used inthis system. Generator 24 contains a supply of water into which ammoniagas has been absorbed. Heater 30 serves to raise the temperature of thewater mixture by injection of heat Q₃ so that ammonia gas is desorbedinto conduit 8. The ammonia gas is converted to a liquid in condenser 10by removing heat energy from the vapor. The liquid ammonia proceedsthrough conduit 12 to expansion valve 14. Expansion valve 14 allows theliquid to expand to a lower pressure thereby being converted to thevapor state in conduit 16 and evaporator 2. The process of vaporizationcools the evaporated gas allowing it to absorb heat from enclosure 18 bymeans of evaporator 2. The ammonia vapor in conduit 4 is thereby warmedto nearly the temperature of enclosure 18. The relatively warm ammoniagas in conduit 4 is introduced into absorber 20 where it is readilyabsorbed into the water. Pump 22 is used to pump the water containingthe absorbed ammonia vapor to generator 24. Throttle valve 26 isutilized to circulate the water in generator 24 back to absorber 20.Absorber 20 gives up heat Q₄. Since a certain amount of the ammoniavapor which is absorbed in the water in absorber 20 is desorbed from thewater in generator 24, the water which is returned to absorber 20 fromgenerator 24 is relatively free of ammonia vapor. The key to theoperation of such an ammonia/water absorption system is the molecularattraction between the absorbent (water) and the refrigerant (ammonia).The molecular attraction is strong enough to allow the refrigerantmolecules to be taken out of the vapor phase and to put them into theliquid phase thereby releasing the heat of condensation plus anadditional heat of solution. This is the basis of operation forabsorption process refrigeration systems and enables replacement of themechanical compressor which is found in vapor compression systems suchas pump 6 and motor 5, as shown in FIG. 1. The absorption process ofFIG. 3 takes place in the low pressure region of the refrigerationcycle. The solution containing both the sorbate and sorbent is thenpumped to the generator on the high pressure side where ammonia isvaporized off by the addition of heat Q₃. The sorbent recirculatesthrough second throttle valve 26 back to the low pressure side where itpicks up more refrigerant. Meanwhile, the refrigerant released by heatregeneration in the generator circulates back through the normal pathjust as it did in the vapor compression cycle of FIG. 1. The work doneby pump 22 in the absorption cycle of FIG. 3 is negligible because thepump does not compress vapor but merely pumps a liquid from a low to ahigh pressure. In fact, the pump is eliminated in some existingliquid-liquid absorption refrigerators. Such a system is shown in FIG.4.

FIG. 6 illustrates a rudimentary and theoretical application of the pumpof the invention in a refrigeration system. By making a directcomparison it may be seen that the apparatus in dashed box 28 of FIG. 3is replaced in FIG. 6 by pump 32 of the invention comprising adsorbent50, plenum 54, plenum 58, heat adsorbing plate 60 and transparentsurface 62. Condenser 10, throttle valve 14 and evaporator 2 areidentical to those of the system of FIG. 3. Pump 32 serves to adsorbwarm low pressure vapor from conduit 4 and deliver a higherpressure-higher temperature vapor into conduit 8 just as wasaccomplished by apparatus 28 of FIG. 3. The rest of the system of FIG. 6operates in the same way as those of FIGS. 1 and 3. However, there aresome practical problems involved in the use of pump 32 in thisapplication. It will be clear that there is a large total pressuredifference required across pump 32. This pressure gradient inducesrelatively high stresses in adsorbent 50, heat adsorbing plate 60 andtransparent means 62. Clearly, it would be advantageous to reduce thesepressures in order to make pump 32 less expensive and less complicatedto manufacture. FIG. 7 illustrates a refrigeration system in which thisproblem is solved.

The refrigeration system of FIG. 7 incorporates some of the aspects andfeatures of the Servel, Inc. refrigeration system, previously described.(See FIG. 4.) In addition to a sorbate and an adsorbent, the system ofFIG. 7 also utilizes a neutral gas for purposes of equalizing totalpressure throughout the system, such as the hydrogen gas used in theServel, Inc. system of FIG. 4. For purposes of illustration it will beassumed that the system of FIG. 7 utilizes water as a refrigerant andhydrogen as a neutral gas.

It will be understood that water has relatively low vapor pressurecharacteristics which will limit mass flow in a closed system such asthis one. A more significant amount of cooling would be provided by arefrigerant such as Freon 113 which has a much higher vapor pressure,yet is a liquid at ambient temperature and pressure conditions. It willbe further understood that other readily available commercialrefrigerants may also be used and that references to water and watervapor in the present description are only illustrative of otherrefrigerants which may also be used.

According to Dalton's rule of partial pressures, the liquid or vaporpressure of water in the various parts of the system plus the hydrogenpressure in that portion of the system will always equal a given totalpressure. This may be expressed as:

    P.sub.T =P.sub.PV +P.sub.PH

where:

P_(T) =total pressure

P_(PV) =partial vapor pressure of water

P_(PH) =partial pressure of hydrogen gas.

The system of FIG. 7 is evacuated and then water and hydrogen areintroduced in a proportion which will be well known to one skilled inthe art of refrigeration. Generally, the water will seek the lower(gravitational) levels of this system and the hydrogen will migrate tothe higher levels of the system due to the density differences betweenhydrogen and water. The total pressure P_(T) is chosen to be equal toatmospheric pressure, about 14.7 pounds per square inch. This enablesthe system to operate under zero total pressure gradient with respect tothe ambient pressure outside of the system. The advantage of such anarrangement lies in the fact that the large flat surfaces such astransparent member 62, heat absorbing plate 60 and adsorbent 50 may beconstructed so that they only need to support their own weight. It willbe understood and well known by one skilled in the art that while P_(T),the total pressure throughout the system, is equal; the partial vaporpressures of water in the various parts of the system will be quitedifferent. This will become more apparent as the system is furtherexplained.

As heat absorber plate 60 is exposed to a radiant heat source, eitherthe sun or some other source, the upper surface of adsorber 50 adjacentto plenum 58 warms up and the partial pressure in plenum 58 increasesbecause of the increased heat energy. Water vapor in plenum 58 begins torise in conduit 8 and proceeds to condenser 10 where it is cooled byambient air and converted to liquid form. The heat of condensation istransferred from condenser 10 at Q₂. The hydrogen in the system isunaffected by the additional heat except that it may expand somewhatthereby marginally raising the total pressure in the system. In systemswhere it is deemed to be unadvisable to allow this expansion to createhigher pressure, a simple "breathing" expansion chamber 13 may beutilized to solve that problem. The water which condenses in condenser10 flows through conduit 12 to liquid trap 15. When the system isstabilized in a fully operable condition, no liquid flows beyond liquidtrap 15. Water vapor is formed from the liquid in liquid trap 15 due tothe lower vapor pressure beyond that point and flows through conduit 16to evaporator 2. The conversion of water from liquid to vapor state inconduit 16 causes the water vapor to cool. This is a result of theconversion of sensible heat to the latent heat of vaporization.Accordingly, the water vapor in evaporator 2 is relatively cold. Thisallows heat transfer to take place from environment 18 throughevaporator 2 heat exchanger fins to the water vapor therein. Thus, thewater vapor at the exit of evaporator 2 in conduit 4 is nearly at thetemperature of environment 18. The relatively warm water vapor rises inplenum 54 of pump 32. Adsorber 50 is made of a hygroscopic material suchas silica gel, Vycor porous Glass or an oxide of metal. Therefore, itattracts the water vapor molecules out of plenum 54.

As the gas/vapor mixture rises in plenum 54, moisture is adsorbed intoadsorber 50 and exothermic heat (heat of adsorption Q₄) is given up. Theheated gas/vapor mixture is urged to the upper end of plenum 54 byreason of the tendency of the warm gas to rise. The warm, dry gas fromplenum 54 is fed through heat exchanger 9 to further reduce thetemperature toward ambient by releasing heat energy Q₄. This nearambient temperature dry gas is then introduced into conduit 16 at apoint just beyond liquid trap 15 and the very low vapor pressure thuscreated at that point causes the liquid in liquid trap 15 to readilyevaporate in the dry gas. As has been previously described, the latentheat of vaporization lowers the gas temperature going into evaporator 2.

The water vapor from plenum 54, which was adsorbed by adsorber 50, isde-adsorbed into plenum 58 under the influence of heat source Q₃. Thus,the gas moving upward in plenum 58 becomes supersaturated with watervapor. The partial water vapor pressure in plenum 58 is increased andthe supersaturated gas moves through conduit 8 to condenser 19.Condenser 10 cools the gas/vapor mixture and causes much of the watervapor to condense to a liquid state. The gas/vapor mixture that is leftmoves through conduit 51 to the lower or input end of plenum 58. Theliquid water from condenser 10 moves through conduit 12 to liquid trap15. It will also be understood that hydrogen in the system will help tofill the conduits of the system. Therefore, the conduits will operate atP_(T), the total pressure of the system, about 14.7 pounds per squareinch absolute.

The pump of the invention may also be utilized in an open cyclerefrigeration system such as is illustrated in FIG. 8. The pump of theinvention is used to dry air which will then be used for cooling anenvironment. Relatively moist warm air is introduced into plenum 54where moisture is removed by adsorber 50 as has been before described.The relatively dry air moves through duct 72 under urging of fan 74.Water vapor is injected into the dry air by spray nozzle 76. A reductionin air temperature is caused by the heat of vaporization required forthe vaporization of water introduced by spray nozzle 76. The air, nowcooled and carrying a relatively higher moisture content, is injectedinto environment 78 where ambient heat energy warms the air. The warm,moist air now moves through duct 80 back to plenum 54 and the cyclebegins again. As water vapor from the air is adsorbed by adsorber 50,the heat of adsorption is carried away by heat exchangers 82. Ambientair at a lower temperature is moved under the urging of fan 70 throughplenum 84. This ambient air carries off the heat of adsorption from heatexchangers 82 through duct 86. This air is now relatively warm andmoist. It is channeled through duct 88 to heat storage system 90 whichmay comprise a rock pile or similar granular material contained in aporous container. Alternatively heat storage device 90 may be comprisedof relatively small containers of water so arranged so that ambient airmay circulate freely through them. Fan 92 urges ambient air throughplenum 58. Water in adsorber 50 is desorbed into the air moving throughplenum 58. This moisture-laden air is then transported through duct 94and duct 88 to storage device 90. Of course, it will be understood thatadsorber 50 is heated on the side adjacent to plenum 58 by a heat sourcesuch as the sun. At those times when the sun is obscured either by theearth or by the environment, fan 92 may be reversed to draw warm air outof heat storage device 90 in order to provide the necessary temperaturegradient across adsorber 50 to provide the pumping action. Since airdrawn from heat storage device 90 is relatively dry, there is no problemwith excessive partial vapor pressure in plenum 58.

In an open cycle refrigeration system such as has been described, supra,it will be clear to one skilled in the art that large quantities of airmust be moved because of the relatively low partial vapor pressuresinherent in the use of water as a refrigerant. It will also be clearthat it is necessary to utilize mechanical devices such as fans 70, 74and 92 to move the air through the system. Of course the amount of airto be moved will depend on the volume of the environment to becontrolled as will be well understood by one skilled in the evaporativecooling art. The system of FIG. 8, however, has a large advantage overclassical evaporative cooling systems. For example, in typicalevaporative cooling systems the ambient humidity must be very low inorder to have an effective operating system. In the system of FIG. 8 thepump of the invention is providing a source of dry air which wouldotherwise not be available. It is advantageous because it operatescontinuously without moving parts, that is, the removal of moisture fromthe air is not accomplished in a batch process manner. This enables thesystem of FIG. 8 to be operated in climates where evaporative coolerswould not otherwise be effective. It will also be clear to one skilledin the art that a condenser could be placed in duct 88 of the system toreclaim the water vapor from the air moving therein in the form ofliquid. This liquid water could be recycled and used in the waterinjection from water nozzles 76. In this manner the water used forcooling in the system would be restrained to a closed loop. Only thatwater not condensed in the above suggested alternate condenser would belost. The alternative system utilizing the condenser in duct 88 would beof special importance in those climates where a plentiful water supplyis not available.

Clearly, other applications for the invention described herein will beapparent to those skilled in the art. Various other modifications andchanges may be made to the present invention from the principles setforth and described above without departing from the spirit and scopethereof as encompassed in the accompanying claims.

What is claimed is:
 1. In a refrigeration apparatus having an evaporatorfor absorbing heat, a condenser for rejecting heat, a refrigerant and apump, the improvement in the pump comprising:microporous means having atleast two working surfaces, said microporous means for adsorbing a vaporfrom a lower vapor pressure environment on a first of said at least twoworking surfaces and for desorbing the vapor to a higher vapor pressureenvironment from a second of said at least two working surfaces, saidsecond surface being in heat energy communication with a heat source toprovide a higher temperature at said second surface with respect to saidfirst surface, said microporous means having pore sizes in the range offrom 10⁻⁶ to 10⁻⁷ centimeters for providing high adsorption and surfacediffusion characteristics.
 2. The improvement according to claim 1wherein said pump means is made of a hygroscopic material.
 3. Theimprovement according to claim 1 wherein said another side is madewarmer than said one side by application of heat energy to said anotherside.
 4. The improvement according to claim 1 wherein the refrigerantincludes a neutral gas for equalizing the total pressures in theapparatus.
 5. The improvement according to claim 3 wherein said heatenergy is supplied by a solar collector.
 6. The improvement according toclaim 2 wherein said hygroscopic material is silica gel.
 7. Theimprovement according to claim 2 wherein said hygroscopic material is anoxide of metal.
 8. The improvement according to claim 2 wherein saidhygroscopic material is Vycor Glass.